In communication networks, services with a wide range of traffic characteristics and quality of service requirements may share the bandwidth of a physical or logical network interface. Examples of services with different requirements are voice, video, best effort and control messaging. A service can have a minimum rate, which is guaranteed in most cases. However, in some applications, e.g. broadband aggregation, the guaranteed minimum rate is oversubscribed, i.e. the minimum rate cannot be guaranteed at every time, causing reduced quality of service, e.g. increasing the latency for a service, in periods with exceptionally high bandwidth demands.
Assume a tree hierarchy where the root represents a 100 Mbps Ethernet interface; the children of the root are virtual local networks (VLANs); and each VLAN has two queues representing leaves in the tree, where a queue stores packets belonging to a service. Further, assume that each VLAN has a maximum rate of 8 Mbps and that one of the two queues has a minimum bandwidth guarantee of 5 Mbps. If minimum rate oversubscription is not allowed, then the 100 Mbps Ethernet interface cannot support more than 20 VLANs, since the sum of minimum bandwidth guarantees across all VLANs is: 5 Mbps*20<=100 Mbps. On the other hand, if oversubscription is allowed, more than 20 VLANs can be supported.
Since not all users are active at the same time, oversubscription can be handled by statistical multiplexing, whereby the sum of allocated minimum rates in the scheduler may exceed the total available rate.
However, situations may exist where the sum of demanded minimum rate exceeds the sum of allocated minimum rate. Even if such situations only may occur with a small probability, it is desirable to be able control those situations.
US2005/0249220 A1 to Olsen et al. describes a hierarchical traffic management system and method ensuring that each of multiple queues is guaranteed a minimum rate, that excess bandwidth is shared in accordance with predefined weights, that each queue does not exceed a specified maximum rate, and that the data link is maximally utilized within the maximum rate constraints.
In US2005/0249220 A1 to Olsen et al., each queue or node has two sets of attributes; enqueue attributes and dequeue attributes. The enqueue attributes control how data packets enter a queue, and as such control the depth of the queue. The dequeue attributes control how data packets exit the queue, and as such control scheduling of the queue with respect to other queues. Further, Olsen et al. describe minimum rate propagation which allows child nodes to be configured with a minimum rate, even though the parent node does not have an equal or greater minimum rate. By the minimum rate propagation, the parent node has a conditional minimum rate guarantee, meaning that when traffic is present on the child node that has a minimum rate guarantee, the parent also has the minimum rate guarantee to be used only for traffic coming from the child with the guarantee.
The minimum rate propagation disclosed by Olsen et al. provides efficiency in applications where oversubscription is common and where it is not possible or desirable to give each parent node its own guarantee, yet delivery of some guaranteed service for some child node services is required.
One drawback with the method and system disclosed by US2005/0249220 A1 to Olsen et al. is that priorities are only propagated from a child node to a parent node and not further in the hierarchy. Thus it is not possible to, in an accurate way, handle cases in which the sum of minimum rates in child nodes are higher than the sum of minimum rates in parent nodes. Thus, Olsen et al cannot handle aggregation services and therefore not controlling bandwidth allocation in case of minimum rate oversubscription. Another drawback is that the priority attribute is associated with a single user defined bandwidth, whereby any traffic up to this bandwidth is regarded as priority traffic and is given priority over other queues of a lower priority, causing bandwidth to be distributed among the traffic in high priority queues in dependence on the scheduling algorithm used.
US2007/0104210 A1 to Wu et al. describes dynamic management of buffers and scheduling of data transmission with minimum and maximum shaping of flows of data packets in a network device so that all of the output bandwidth can be fairly and fully utilized according to set requirements.
For each queue, during minimum bandwidth guarantee shaping, the scheduler will be selected based on round robin scheduling or strict priority scheduling, based on a separate minimum bandwidth strict priority register.
After satisfying minimum bandwidth guarantees, each queue is entered into a maximum bandwidth allowable region, where the scheduler will use either weighted deficit round robin (WDRR) or strict priority (SP) to pick a data packet from different quality of service (QoS) queues.
Neither US2007/0104210 A1 to Wu et al. disclose a method or a system capable of handling aggregation services and the disclosed method and system is therefore not capable of controlling bandwidth allocation in case of minimum rate oversubscription.